Many neural cells in the visual systems of lower animals have been shown to be "tuned" for maximum response to specific stimulus configurations or events. For example, some units respond with great vigor to a border or edge of particular orientation and are relatively unresponsive to the same border when it is rotated through some small angle. The possibility that our own visual systems contain similar mechanisms warrants careful study because the properties of such stimulus analyzers may provide important insights into the characteristics of human vision. The proposed research has two major, related objectives. First is the psychophysical study of visual mechanisms responsive to movement and contour properties in human vision. The second objective is the explication of various characteristics of stimulus discriminability in terms of the sensitivity profiles and other properties of the underlying stimulus analyzing mechanisms.